Stars

Molecular Clouds

As the gas and dust
of the disc of a galaxy is squashed by the spiral arms,
the gas condenses onto stardust grains to form
molecular clouds, so-called because they contain molecules,
which we explain later in this story. These are so dense that light cannot pass
through them. They are the dark areas we see when we look at the Milky Way. When seen through a
telescope they often reflect the light of nearby stars.